Because we're using maxValue as a prop to useDateTimeRangePicker which is set to now(getLocalTimeZone()) (to prevent a user from setting and end time beyond the current moment). It's continuously causing re-renders in any component that calls it.
It'd obviously defeat the point if we memoized the current time. I thought we could call now() within the DateRangePicker itself at change time but it seems like the props are just forwarded to useDateRangePickerState. We can investigate further, maybe there's react-aria feature that'll handle this for us.
Don't think this is actually the reason, since now() will just get called when the component re-renders. Something else is afoot.